1. Field of the Invention
The invention relates to a connector assembly with BGA type contacts, and particularly to a connector assembly with an interposer plate for implantation of solder balls thereon.
2. The Related Art
A CPU is a necessary component of a personal computer. For economic reasons the CPU is electrically connected to the mother board by a socket connector. Conventional socket connectors are disclosed in U.S. Pat. Nos. 5,399,108, 5,489,218 and 5,679,020. The conventional socket may be a unitary housing providing a LIF (Low Insertion Force) application or a two piece housing providing a ZIF (Zero Insertion Force) application. Recently SMT (surface mounting technology) has become popular thus such conventional sockets having pin type contacts for wave-soldering attachment to the board can no longer facilitate manufacture.
Ball type contact portions, i.e. BGA (Ball Grid Array), for SMT mounting to a PC board is becoming an increasingly common technique for attaching IC chips. One approach involves attaching ball-like contact leg sections, i.e. solder balls, on a bottom surface of the socket instead of the conventional pin type contact tails. However, the material of the PC board and that of the socket are different. Implantation of the solder balls onto the bottom surface of the socket causes difficulties in manufacture. Additionally, the socket is made by ejection molding and has an inherently loose tolerance in comparison with the PC board which is precisely made with a tight tolerance. The inherent inferior tolerance of the socket may result in positional and coplanarity problems of the implanted balls. Moreover, due to different material properties between the PC board and the socket, CTE (coefficient of Thermal Expansion) mismatch between the socket and the PC board on which the socket is mounted through the solder balls may overstress the solder balls causing rupture of thereof during manufacture.
Therefore, an object of the invention is to provide an improved connector assembly with a BGA (Ball grid Array) contact arrangement which overcomes the problems discussed above.